Contacting-making system for two printed circuit boards

ABSTRACT

In order, in the context of making contact between two printed circuit boards ( 2, 4 ), to ensure a high positioning accuracy of their two contact regions ( 8 ) with respect to one another, the two contact regions ( 8 ) are three-dimensionally structured complementarily with respect to one another. A mask ( 12 ) having cutouts ( 14 ) for contact elements ( 10 ) of the two printed circuit boards ( 2, 4 ) is preferably provided. This positioning using the conductor track pattern and independently of a contact-making housing ( 26 ) has the advantage that the positioning accuracy is unaffected by tolerances between the conductor track pattern and the contact-making housing ( 26 ).

[0001] The invention relates to a contact-making system for two printedcircuit boards which, for reciprocal contact-making, each have a contactregion with contact elements.

[0002] A printed circuit board has a number of conductor tracks viawhich a functional element or an assembly is supplied and/or driven. Inorder to wire up and interconnect the individual functional elements orassemblies, for example in an on board electrical system of a motorvehicle, connecting elements or contact-making systems are provided viawhich printed circuit boards are connected to one another or a printedcircuit board is connected to a conventional connector. The printedcircuit boards have a rigid supporting layer, for example, on which theconductor tracks are applied or they are designed as flexible printedcircuit boards for example in the form of conductor sheets with applied,in particular etched, conductor tracks.

[0003] Reliable and permanent contact-making is always necessary inorder to maintain the functional reliability. This is particularlyapplicable in the automotive sector, where severe temperaturefluctuations and vibrations occur. What is crucial for reliablecontact-making is that the individual contact regions and contactelements of the elements that are to be connected to one another arepositioned with great accuracy with respect to one another in thejoining-together process. A high positioning accuracy has the advantagethat the contact areas overlap one another to a great extent, a lowcontact resistance thereby being attained. On the other hand, thepositioning accuracy has the effect that the spacing from neighboringcontact elements is kept large enough to keep the risk of short circuitslow.

[0004] The task of positioning a printed circuit board relative to afurther printed circuit board or else to the contact areas of aconnector is generally undertaken by a contact-making or connectorhousing. EP A 0 849 120, EP A 0 717 462, DE A 199 05 064 and DE U 298 23576 disclose special contact-making housings for positioning printedcircuit boards.

[0005] EP A 0 849 120 provides for the printed circuit board to bepushed into a slotted housing in such a way that a cutout of the printedcircuit board in a contact region is aligned with a channel guidedthrough the housing. Contact is made with the conductor track via acontact pin which is guided through the channel and the printed circuitboard. The contact pin has a larger diameter than the cutout, therebyensuring that contact is made. Therefore, the positioning is effected byway of the interaction of the contact pin guided in the channel with thecutout.

[0006] EP A 0 717 462 provides for the printed circuit board to bepushed into a conically tapering receptacle region of a contact-makinghousing, so that the printed circuit board is slightly curved and cannotbe shifted within the contact-making housing. The printed circuit boardis thus guided by the contact-making housing in this case.

[0007] DE A 199 05 064 and DE U 298 23 576 are concerned with the mutualcontact-making of two printed circuit boards. Here, too, the task ofpositioning is undertaken by a contact-making housing. In accordancewith DE A 199 05 064, the printed circuit boards are clamped in betweentwo clamping jaws, centering pins being integrally formed on one of theclamping jaws, which pins are guided through cutouts in the printedcircuit boards and engage in corresponding centering holes on theopposite clamping jaw. The clamping jaws have a structured surface whichis impressed on the printed circuit boards in the form of an undulatoryprofile. DE U 298 23 576 discloses inserting one printed circuit boardinto a cutout in an upper housing half and positioning the secondprinted circuit board with respect to a lower housing half via centeringpins of the latter, the centering pins of the lower housing halfengaging in centering holes in the upper housing half. In order toensure a sufficient contact pressure for a good contact, the lowerhousing half has spring means which act on the contact elements of theprinted circuit boards. Contact bulges are provided for this purpose,the spring means engaging in said contact bulges, so that the contactbulges are pressed against the individual contact elements of the secondprinted circuit board.

[0008] What all the known embodiments have in common is the fact thatthe positioning is effected via the contact housing. Therefore, thepositioning accuracy depends inter alia on the dimensional accuracy ofthe housing and, in particular, on the tolerances of the conductortracks relative to the mechanical positioning elements. Reducing thetolerances for the purpose of increasing the positioning accuracy canonly be achieved by complicated means, such as, for example, mechanicaldesign changes to the contact-making housing.

[0009] An alternative option for positioning is optical positioncontrol, in which an automatic component-mounting machine determines theposition optically. However, both technically and economically thismethod is practical only for undetachable permanent standardconnections.

[0010] The invention is based on the object of specifying acontact-making system for two printed circuit boards with which a highpositioning accuracy can be achieved.

[0011] The object is achieved according to the invention by means of acontact-making system for two printed circuit boards which, forreciprocal contact-making, each have a contact region with contactelements, in which case, for the positioning of the printed circuitboards, the two contact regions are three-dimensionally structuredcomplementarily with respect to one another.

[0012] The essential underlying idea is to be seen in the fact that thefunction of positioning is taken care of by the contact regionsthemselves, so that positioning relative to housing parts is obviated.This necessarily obviates the problems which stem from tolerancesbetween the conductor track pattern and the positioning elements. Thus,instead of positioning relative to a housing, the conductor trackpattern itself is used as positioning element. The specialthree-dimensional structuring is provided for this purpose, throughwhich, on account of the complementary configuration in particular ofcontact elements that are to be contact-connected to one another,automatic positioning is effected in the joining-together process. Thetwo contact regions thus have elevations and depressions which definetheir position with respect to one another. The complementarythree-dimensional structure permits a simple, reliable and fastjoining-together process with high positioning accuracy of the twoprinted circuit boards.

[0013] In a preferred embodiment, the contact elements on the printedcircuit boards form an elevation, so that the printed circuit boards arespaced apart from one another in the joined-together state. In thiscase, the height is chosen in such a way that, under a specific contactpressure, all the contact areas of the contact elements touch oneanother and further elements on the printed circuit board such as e.g.solder resist or uncovered conductor tracks do not touch one another,high functional reliability thereby being achieved.

[0014] In this case, the contact elements are preferably embodied asplanar structural parts made of conductive material and are eitherapplied in the form of laminae to the conductor tracks, for example by asoldering operation, or else formed by an embossing operation. If onlylow currents are to be transmitted, then carbon-filled plastic is alsosuitable, in particular, as a material for the contact elements. By wayof example, the contact elements are embodied solidly in the form of acube, a parallelepiped or a disk. Their contact area is preferablyroughened in order to reduce the contact resistance. As an alternativeto a contact area of planar design, complementary contact elements havea bulge and a complementary indentation in the region of their contactareas. This shaping results in self-centering of the contact elementpair.

[0015] The contact elements, for forming the three-dimensionalstructure, preferably have different heights, the total height of thecontact element pairs formed by complementary contact elements beingidentical. The different heights serve for positioning and the constanttotal height ensures that reliable contact is made with all the contactelements.

[0016] For the highest possible positioning accuracy, it is advantageousto provide at least two complementary contact element pairs which have alarge spacing from one another; in particular, they are arranged onopposite end regions of the printed circuit boards.

[0017] In order to achieve reliable and permanent contact-making, apreferred embodiment provides for at least one contact element of acontact element pair to be of elastic design. In particular, the contactelement is configured resiliently or as a spring. For this purpose, thecontact element is, for example, constructed in two parts, the firstpart undertaking the actual contact-making and the other part ensuringthe elasticity. Within a certain tolerance range, height differencesbetween the two printed circuit boards can be bridged without difficultyby virtue of the elastic or resilient design.

[0018] For the same purpose, simultaneously or alternatively at leastone of the printed circuit boards is of elastic design, so that theheight tolerance compensation is automatically performed additionally oralternatively by one or by both printed circuit boards in thejoining-together process. The printed circuit board of elastic design isthus pliant or flexible.

[0019] In accordance with a further preferred embodiment, in addition tothe function purely of contact-making, a further function is alsointegrated in the contact region. For this purpose, at least one of thecontact elements comprises an electronic component, which may be eitheran active or a passive component. By way of example, this componentrealizes the function of current limiting, of a series resistor, ofrectification or of overtemperature protection. If a piezoactive elementis used as the component, then a pressure-sensitive contact element, forexample, is realized.

[0020] In a particularly advantageous refinement, a mask for arrangementbetween the printed circuit boards is provided, which has passageopenings for the contact elements. Such a mask is composed ofnon-conducting material such as plastic or ceramic. As a result, on theone hand reliable insulation of neighboring contact elements is realizedand, on the other hand, the relative movement of the printed circuitboards with respect to one another is limited within the productiontolerances. Since the printed circuit boards are preferably pressedtogether by means of a contact-making housing, all degrees of freedom ofmovement of the printed circuit boards with respect to one another arelimited and, consequently, reliable and permanent contact-making isachieved.

[0021] In preferred alternative embodiments, the mask is embodied eitheras an autonomous element in the form of a stencil for insertion betweenthe two printed circuit boards or as a constituent part of at least oneof the two printed circuit boards. In the first case, the stencil isparticularly simple and light to produce and, in particular, it is partof a contact-making housing which is preferably a plasticinjection-molded part. In conjunction with the stencil, thecontact-making housing at the same time performs a protection functionfor the contact region, provides for strain relief and brings about asufficiently high contact pressure.

[0022] If the mask is embodied as a constituent part of one of theprinted circuit boards, then the number of structural parts is reduced.For this purpose, a resist, for example, is applied to the printedcircuit board and is removed in the region of the contact-makingelements using suitable methods.

[0023] Preferably, with the printed circuit boards joined together, thethickness of the mask maximally reaches the total height of the contactelement pairs, thereby ensuring that contact is made with the individualcontact elements. For this purpose, the mask has, for example, athickness which is slightly less than the total height, thereby ensuringreliable guidance of the contact elements through the mask.

[0024] The masks is preferably made of an elastic material and has, inparticular, a thickness which exceeds the total height of the contactelement pairs. When the printed circuit boards are joined together, theelastic mask is then compressed and preferably performs a sealingfunction, so that the contact region is sealed toward the outside.

[0025] In order to produce reliable contact-making, a contact pressureis preferably exerted on the printed circuit boards by a contact-makinghousing in the joined-together state. In particular, the contact-makinghousing has an elastic region in the contact-making region, so thatheight tolerance compensation can be effected in the event ofproduction-dictated height differences between the individual contactelements. The contact-making housing thus acts with a spring force onthe contact-making region.

[0026] The concept of the intrinsic positioning of the contact regionswith respect to one another by means of complementarily designed,three-dimensional structures is preferably also provided for printedcircuit boards with which contact can be made on both sides and whichare arranged in a layered manner one above the other. In particular,three to five printed circuit boards of this type are arranged in alayered manner.

[0027] Exemplary embodiments of the invention are explained in moredetail below with reference to the drawing, in which, in diagrammaticillustrations in each case:

[0028]FIG. 1 shows a perspective view of two printed circuit boards withstencil,

[0029]FIG. 2 shows two printed circuit boards in a sectional view withstencil directly before the joining-together process,

[0030]FIG. 3 shows the two printed circuit boards as shown in FIG. 2 inthe joined-together state,

[0031]FIG. 4 shows two printed circuit boards in a lateral sectionalview with resiliently configured contact elements,

[0032] FIGS. 5-7 show alternative embodiments of a complementarythree-dimensional structure of the printed circuit boards in the contactregion,

[0033]FIG. 8 shows a plan view of a printed circuit board with anarrangement of contact elements, and

[0034]FIG. 9 shows a contact-making housing with clamped in printedcircuit boards.

[0035] In accordance with FIG. 1, a first and a second printed circuitboard 2, 4 each have a number of conductor tracks 6 which lead into acontact region 8. In this case, a contact element 10 is assigned to eachindividual conductor track 6 in the contact region 8. Furthermore, amask 12 designed as a stencil and serving for arrangement between theprinted circuit boards 2, 4 is provided, which mask has cutouts 14 forthe contact elements 10.

[0036] The printed circuit boards 2, 4 are designed as stiff printedcircuit boards or else as flexible printed circuit boards, for examplein the form of conductor sheets. The contact elements 10 have adifferent height, so that the contact region 8 of each printed circuitboard 2, 4 has a three-dimensional structure. In this case, the contactregions 8 are structured in such a way that they have a mutuallycomplementary three-dimensional structure. In the exemplary embodimentas shown in FIG. 1, this is achieved by the provision of two contactelement types, namely a high contact element 10A and a low contactelement 10B, which are arranged alternately next to one another. In thiscase, a respective high contact element of the first printed circuitboard 2 is provided for making contact with a low contact element 10B ofthe second printed circuit board 4. The individual contact elements 10thus engage in one another virtually like teeth or in crenellatedfashion. As a result, the two printed circuit boards 2, 4 are positionedwith respect to one another and lateral shifting is not made possible.The mask 12 additionally precludes shifting in the longitudinaldirection and, moreover, the individual contact elements 10 areinsulated from one another by the mask 12.

[0037] The contact elements 10, in particular the high contact elements10A, are embodied as laminae, for example, which are applied to therespective printed circuit board 2, 4 by soldering. Correspondinglythinner laminae are provided for the low contact elements 10B, or theyare formed by widening the conductor tracks 6 leading to them.

[0038] For a high positioning accuracy and in order to keep theproduction tolerances as small as possible, it is extremely expedient ifthe individual contact elements 10 are applied to the positions providedfor them on the printed circuit boards 2, 4 with high accuracy. A highaccuracy is achieved by automatic component-mounting machines, forexample, which determine the position using optical methods andsubsequently solder the contact elements 10 to the printed circuit board2, 4. Given an appropriate embodiment of the soldering method, theeffect of self-centering governed by the surface tension of the liquidsolder can be utilized for accurately aligning the individual contactelements 10. A high accuracy can also be attained by means of anelectrochemical plating method. This method is particularly suitable forrelatively small connection grids, since the accuracy of the platingoperation is particularly high. In order to achieve the thinnestpossible dimensions, a stamped out sheet is preferably used as mask 12in this case. A particularly thin and flexible contact point can begenerated in this way.

[0039] The contact-making operation is effected as shown in FIGS. 2 and3, according to which the two printed circuit boards 2, 4 are alignedparallel to one another in the contact region 8, so that a high contactelement 10A is in each case aligned above a low contact element 10B. Inaccordance with this exemplary embodiment, the mask 12 is fixedlyapplied to the first printed circuit board 2 and forms a unit with thelatter. In this case, the thickness D of the mask 12 is dimensioned insuch a way that it is greater than the low height Hl of the low contactelements 10B and, at the same time, less than the large height H2 of thehigh contact elements 10A. It is important for the thickness D to begreater than the height Hl, so that the mask 12 prevents the twoconductor tracks from slipping laterally with respect to one another, inorder to attain a high positioning accuracy. On the other hand, thethickness D in the mounted end state should not exceed the total heightH of a contact element pair 10A, 10B, resulting from the sum of the twoheights Hl and H2. This ensures that the two contact elements 10B, 10Aactually come into contact by way of their contact areas. The mask 12 ispreferably of elastic design, that is to say compressible, so that—as analternative to the embodiment as shown in FIGS. 3 and 4—it can have athickness D greater than the total height H before the printed circuitboards 2, 4 are joined together. When the printed circuit boards 2, 4are joined together, a contact pressure is exerted, so that the mask 12is compressed, and the respective contact element pairs 10A, 10B comeinto contact with one another. At the same time, the mask 12 bears bothon the first printed circuit board 2 and on the second printed circuitboard 4 and thus ensures that the contact region 8 is reliably sealedfrom its environment.

[0040] In accordance with FIGS. 2 and 3, one of the high contactelements 10A is designed as a special contact element 10C whichcomprises or forms an electronic component. This electronic componentmay be embodied as an active or passive component and serves, forexample, for current limiting or else as a temperature or pressuresensor.

[0041] Since production-dictated differences occur in connection withthe heights H1 and H2 of the individual contact elements 10A, 10B,height compensation is extremely expedient for reliable contact-making.This can be done in various ways which can be used alternatively or incombination. First, by way of example, the contact elements 10themselves are of elastic design, that is to say, in particular,compressible, so that height differences are compensated upon thejoining-together of the two printed circuit boards 2, 4 under a certaincontact pressure. As a further possibility, one or both printed circuitboards 2, 4 is or are of elastic, that is to say pliant, design, so thatthey are adapted to the required total height H in a position-dependentmanner. In addition to the elastic design of the contact elements 10through a suitable elastic material, the contact elements 10 are ofresilient design, as is indicated in FIG. 4.

[0042] In accordance with FIG. 4, a contact element 10A of a contactelement pair 10A, 10B is in each case configured resiliently and, forthis purpose, has a bent leaf spring 16, for example. This leaf spring16 is connected to the first printed circuit board 2 via a base 18. Theelastic or resilient configuration of the contact elements 10 isalternatively achieved by means of a two-part embodiment with a fixedmetal contact lamina and an elastic support.

[0043] FIGS. 5 to 7 diagrammatically illustrate various possibilitiesfor the design of the three-dimensional structure. In accordance withFIG. 5, only the two outer contact elements 10 of the first printedcircuit board 2 are embodied as high contact elements 10A and all thecontact elements 10 in between are embodied as low contact elements 10B.In a complementary manner to this, the contact elements 10 of the secondprinted circuit board 4 are embodied as high contact elements 10A in thecentral region.

[0044] In accordance with FIG. 6, the high contact elements 10A arearranged in an alternating manner with the low contact elements 10B oneach printed circuit board 2, 4. And in accordance with FIG. 7, thecontact region is again divided into two edge regions and a centralregion, but in this case, in contrast to FIG. 5, three contact elements10A, 10B of the same height H1, H2 are in each case arranged in the edgeregion.

[0045]FIG. 8 shows a particularly advantageous arrangement of thecontact elements 10 in the contact region 8 of the printed circuitboard. The high contact elements 10A are identified by a cross, whilethe low contact elements 10B are represented as a white box. Thearrangement of the contact elements 10 is distinguished by its dense andcompact arrangement. The reliable positioning governed by thethree-dimensional complementary structuring of the contact region 8enables the dense arrangement of the contact elements 10, withoutnegative effects such as, for example, an excessively small overlap ofcontact areas or undesirable contact-making with neighboring contactelements being avoided. The conductor tracks 6 are guided past thecontact elements 10, which are arranged in contact rows 20, in theinterspaces.

[0046] In accordance with FIG. 9, the two printed circuit boards 2, 4are pressed in between an upper housing part 22 and a lower housing part24 of a contact-making housing 26, so that reliable contact-making isobtained through the contact pressure. In order to enable heightcompensation across the contact region 8, the two housing parts 22, 24are not of rigid design but rather have flexurally elastic regions 27and exert a spring force on the two printed circuit boards 2, 4.

[0047] The mask 12 is an integral constituent part of the contact-makinghousing 26 and connects the two housing parts 22, 24 to one another and,just like the housing parts 22, 24, is designed as a plasticinjection-molded part. For this purpose, the mask 12 is connected to thetwo housing parts 22, 24 via a hinge 28 in each case, so that thehousing parts 22, 24 can in each case be folded aside in order to insertthe printed circuit boards 2, 4.

[0048] The preferred configuration in accordance with FIG. 9 limits alldegrees of freedom of movement for the two printed circuit boards 2, 4.To be precise, the two degrees of freedom in the plane of the printedcircuit boards 2, 4 are limited by the three-dimensional structuring ofthe contact elements 10 and also by the arrangement of the mask 12. Thedegree of freedom which is arranged perpendicularly to this area islimited by the contact-making housing 26. Consequently, in thejoining-together process, owing to the three-dimensional complementarystructuring, precise centering is achieved on account of the specialshaping of the conductor track pattern in the contact region 8, which isalso maintained permanently by the special arrangement in thecontact-making housing 26.

[0049] Instead of the multipart design of the contact housing 26, in analternative configuration the contact-making housing 26 is produced byencapsulation by injection-molding or foaming of the contact region 8.

[0050] The above-described embodiments of the three-dimensionallystructured contact region 8 represent particularly preferredconfigurations. However, the three-dimensional structuring is notrestricted to these configurations. Rather, the underlying idea ofpositioning the printed circuit boards 2, 4 using the conductor trackpattern and independently of the contact-making housing 26 can also berealized in alternative ways.

[0051] By way of example, the first printed circuit board 2 has, in thecontact region 8, a cutout or a hole into which or through which acomplementary pin of the second printed circuit board 4 engages orreaches. In this case, the hole and the pin are arranged eithercentrally in the respective contact element 10 or else directly besideit. It suffices if, in this case, one of the contact elements 10 iselevated only slightly from the printed circuit board 2, 4 and the otheris designed to be flat.

[0052] In a further alternative, one contact element 10 of a contactelement pair has a, for example, conical recess in which acomplementarily designed mating piece of the further contact element 10engages. The mating piece is embodied in a cone-like manner, forexample, so that self-centering is effected between the two contactelements 10.

1. A contact-making system for two printed circuit boards (2, 4) which, for reciprocal contact-making, each have a contact region (8) with contact elements (10, 10A C), characterized in that, for the positioning of the printed circuit boards (2, 4), the two contact regions (8) are three-dimensionally structured complementarily with respect to one another.
 2. The system as claimed in claim 1 , characterized in that the contact elements (10, 10A C) on the printed circuit boards (2, 4) form an elevation in such a way that the printed circuit boards (2, 4) are spaced apart from one another in the joined-together state.
 3. The system as claimed in claim 2 , characterized in that the contact elements (10, 10A C) have different heights (H1, H2), the total height (H) of the contact element pairs (10A, 10B) formed by complementary contact elements (10A, 10B) being identical.
 4. The system as claimed in one of the preceding claims, characterized in that at least two complementary contact element pairs (10A, 10B) which have a large spacing from one another are provided.
 5. The system as claimed in one of the preceding claims, characterized in that at least one contact element (10A) of a contact element pair (10A, 10B) is of elastic, in particular resilient, design.
 6. The system as claimed in one of the preceding claims, characterized in that at least one of the printed circuit boards (4) is of elastic design.
 7. The system as claimed in one of the preceding claims, characterized in that at least one of the contact elements (10A) comprises an electronic component (10C).
 8. The system as claimed in one of the preceding claims, characterized in that a mask (12) for arrangement between the printed circuit boards (2, 4) is provided, which has passage openings (14) for the contact elements (10, 10A C).
 9. The system as claimed in claim 8 , characterized in that the mask (12) is embodied as an autonomous element.
 10. The system as claimed in claim 8 or 9 , characterized in that the mask (12) is part of a contact-making housing (26).
 11. The system as claimed in claim 8 , characterized in that the mask (12) is embodied as a constituent part of at least one of the two printed circuit boards (2, 4).
 12. The system as claimed in one of claims 8 to 11 , characterized in that, with the printed circuit boards (2, 4) joined together, the thickness (D) of the mask (12) maximally reaches the total height (H) of the contact element pairs (10A, 10B) formed from complementary contact elements (10A, 10B).
 13. The system as claimed in one of claims 8 to 12 , characterized in that the mask (12) is of elastic design.
 14. The system as claimed in one of the preceding claims, characterized in that a contact pressure is exerted on the printed circuit boards (2, 4) by a contact-making housing (26) in the joint-together state.
 15. The system as claimed in claim 14 , characterized in that the contact-making housing (26) has an elastic region (27) in the contact-making region (8). 